python_{binary,library}{,_host} handle lib property

Have binary and library bp2build convert `libs` to
`deps` for bazel

Bug: 196083751
Test: python_{binary,library}_conversion_test.go
Test: build/bazel/ci/mixed_{libc,droid}.sh
Change-Id: I2d5f6ef2e83dd608910edb7adb2eb9a56d25293c